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Basic Query Operations

MongoDB is a popular NoSQL database that provides high performance, high availability, and easy scalability. It works on the concept of collections and documents. In this tutorial, we'll learn about the basic query operations that you can perform in MongoDB.

1. Understanding MongoDB Querying​

In MongoDB, querying refers to the operation of fetching data from a database. That is, it's a way of searching for specific data by filtering out the information you need.

For MongoDB, queries are structured as a JSON-like document. For example, if you want to find all documents within a collection where the field name equals "John", you would use the following query:

{ "name": "John" }

2. Basic Query Operators​

MongoDB uses operators to perform specific types of queries. These operators are prefixed with a $ sign and can be used in various combinations. Let's look at some basic query operators:

  • $eq: Matches values that are equal to a specified value.
  • $gt: Matches values that are greater than a specified value.
  • $gte: Matches values that are greater than or equal to a specified value.
  • $in: Matches any of the values specified in an array.
  • $lt: Matches values that are less than a specified value.
  • $lte: Matches values that are less than or equal to a specified value.
  • $ne: Matches all values that are not equal to a specified value.
  • $nin: Matches none of the values specified in an array.

3. Basic Query Example​

Let's say we have a collection of books and we want to find all the books published after 2000. We'd use the $gt operator like this:

db.books.find({ "published_year": { $gt: 2000 } })

4. Using Logical Operators​

MongoDB also provides logical operators like $or, $and, $not, and $nor. These can be used to combine multiple query conditions.

For example, if you want to find all books that were either published after 2000 or have more than 500 pages, you would use the $or operator:

db.books.find({ $or: [{ "published_year": { $gt: 2000 } }, { "pages": { $gt: 500 } }] })

5. Querying Subdocuments​

In MongoDB, you can also query nested documents. This is done by using dot notation.

For example, if you want to find all books where the author's name is "John", your query would look like this:

db.books.find({ "author.name": "John" })

6. Querying Arrays​

You can also query fields that contain an array of values.

For example, if you want to find all books that have "fiction" as one of their genres, you would use this query:

db.books.find({ "genres": "fiction" })

Conclusion​

That's it for basic query operations in MongoDB! Remember that the key to mastering MongoDB queries is practice. Try to come up with different scenarios and see how you would structure the queries. Happy querying!